Field current profile

ABSTRACT

An output of a generator may vary according to the speed of the engine, physical characteristics of the engine, or other factors. A profile for a generator that describes a periodic fluctuation in an operating characteristic for the generator is identified. A field current of an alternator associated with the generator is modified based on the profile for the generator in order to counter variations in the output of the generator.

TECHNICAL FIELD

This disclosure relates in general to a field current profile, or moreparticularly, to a field current profile to control output of agenerator.

BACKGROUND

A private residence normally receives power from a utility company. Thereliability of the power company depends on many factors such as theweather, usage spikes, short circuits, accidents or other damage totransmission lines or power stations. Certain locations may beparticularly prone to blackouts. Low lying areas may be susceptible tofloods. Coastal areas may be susceptible to hurricanes. High usagegeographic areas may be susceptible to rolling blackouts.

Any breaks in power utility service may be unacceptable to customers,and some businesses may have mission critical systems, such as computersystems in call centers or refrigerators in grocery stores, that rely onconstant power. In other businesses such as hospitals, lives may be lostif the power to a respirator is interrupted. These customers may rely ona backup source of powers.

One backup source of power is a generator. A generator may produceelectricity at various voltage levels and frequencies. The shape of theoutput is comparable to a sinusoid. However, the output may not be aperfect sinusoid. Certain applications or end users may require a moreideal output from the generator.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary implementations are described herein with reference to thefollowing drawings.

FIG. 1 illustrates an example generator including a field currentcontrol system.

FIG. 2 illustrates an example speed profile for a generator.

FIG. 3 illustrates an example output for the speed profile of FIG. 2.

FIG. 4 illustrates an example modified field current.

FIG. 5 illustrates an example comparison of field current, outputvoltage, and frequency for a generator.

FIG. 6 illustrates the example of FIG. 5 with a modified field current.

FIG. 7 illustrates another example modified field current.

FIG. 8 illustrates an example output for a generator.

FIG. 9 illustrates the example output of FIG. 8 with a modified fieldcurrent.

FIG. 10 illustrates an example regulator circuit.

FIG. 11 illustrates another example regulator circuit.

FIG. 12 illustrates the example regulator circuit of FIG. 11 in a firststate.

FIG. 13 illustrates the example regulator circuit of FIG. 11 in a secondstate.

FIG. 14 illustrates an example duty cycle for the regulator circuit.

FIG. 15 illustrates an example controller of the system of FIG. 1.

FIG. 16 illustrates example flowchart for field current control.

DETAILED DESCRIPTION

An engine-generator set, which may be referred to as a generator or agenset, may include an engine and an alternator or another device forgenerating electrical energy. Example types of generators includetowable generators, portable generators, marine generators, industrialgenerators, residential generators or other standby generators. Agenerator may include a rotor and a stator. The stator may includeoutput windings, and the rotor may include field windings. Otherarrangements are possible.

A generator may generate an output voltage (also referred to as an“output”) having a magnitude. The magnitude of the output voltage asmeasured over a period of time may form a shape or waveform (referred toan “output shape” or as a “shape of the output”) and amplitude. Variousfactors affect the magnitude of the output voltage and thereforecontribute to the shape and/or amplitude of the output of a generator.The shape or amplitude of the output may be a function of the physicaldimensions of the rotor and/or the speed of the engine.

The physical dimensions of the rotor may affect the shape of the output.The magnetic field generated by the rotor by movement relative to thestator may induce a voltage between windings of the stator. When theshape of the rotor is irregular, the voltage of the output is irregular.For many applications, an irregularly shaped output voltage has noeffect on the performance of the system. However, some applications mayhave tight tolerances for the magnitude of the output voltage. In someinstances, the output voltage may be irregular enough to cause flickerin lights powered by the generator. More commonly, many users mayperceive that a regularly shaped output voltage leads to betterperformance of the system irrespective of the actual performance of thesystem.

In addition, speed fluctuations of the engine may affect the shape oramplitude of the output. When an engine is undergoing a power stroke,the engine is applying positive torque to the crankshaft. When thetorque to the crankshaft is more than the torque demanded by thealternator, the crankshaft and the alternator rotor accelerate. When thetorque produced by the engine is less than the alternator demands, thecrankshaft and the alternator decelerate. The additional energy isstored in the rotating crankshaft. Energy from the crankshaft compressesthe gas in the cylinder, and supplies energy back to the crankshaft whenthe gas explodes. Through these cycles of acceleration and deceleration,the crankshaft is speeding up and slowing down, which may createfluctuations in the shape or amplitude of the output.

Additionally or alternatively, the shape or amplitude of the output maybe directly proportional to the field current. The following examplesintroduce field current control to counter or reduce the fluctuations inoutput caused by speed fluctuations of the engine or the mechanicalconstruction of the alternator. The field current of the alternator maybe controlled as a function of the fluctuations in output or predictedfluctuations in output.

FIG. 1 illustrates an example generator 100 including a field currentcontrol system. The generator 100 may include a controller 10, analternator 11, an engine 13, a detection circuit 15, and a field coil17. Optionally, an internal switch (e.g., circuit breaker 23) maycontrol an electrical connection turn the output of the generator 100 onand off. In other examples, the controller 10 may be external to thegenerator 100, and may communicate with and/or control the generator 100through a wired or wireless network or connection. Additional,different, or fewer components may be included.

The controller 10 may identify a profile for the generator 100. Theprofile may describe a periodic fluctuation in one or a combination ofoperating characteristics for the generator 100. The profile may beaccessed from a database or another memory in communication with thecontroller 10. The operating characteristics may include the speed ofthe engine 13 (e.g., speed of the crankshaft), the speed of thealternator 11, or the output (e.g., voltage, current, or power) of thegenerator 100.

The values for the profile may be measured by the detection circuit 15.The detection circuit 15 may be a voltage sensing circuit or a currentsensing circuit to monitor sensor output. The detection circuit 15 mayinclude a sensor for determining the speed of the generator 100.

The sensor may directly detect the movement of a component such as acrankshaft, gear box, transmission, armature, rotor, or anothercomponent. The direct type of sensor may be or include a torque sensor,a deflection sensor, a dynamometer, a positional sensor, or a revolutionsensor.

For example, a deflection sensor may measure a deflection of thecrankshaft or another device. The deflection sensor may include twoposition sensors. The position sensors may be associated with differentsides of the crankshaft. As an example, the sensor may be a positionalsensor (e.g., position sensor or accelerometer) that may measure thechange in rotation of a crankshaft or other component of generator 100.The revolution sensor may be a magnetic sensor that detects a change ina magnetic field, an optical sensor that detects indicia on thecomponent, a contact sensor that detects a tab or protrusion on thecrankshaft, or another component.

Additionally or alternatively, the sensor may indirectly detect themovement of the component. For example, the movement of the componentmay be inferred from the operation of a fuel injected as detected by afuel injector sensor or inferred from fuel consumption as detected by anair to fuel ratio (AFR) sensor. As an example, a fuel injector sensormay measure a quantity of fuel supplied to the engine 13 of thegenerator 100. The quantity of the fuel may be determined based on apulse width value of the fuel injector. The AFR sensor may measure theratio of air to fuel in the engine 13 of the generator 100. The air flowthrough the engine 13 may be calculated based on the ratio of air tofuel and the quantity of fuel.

The controller 10 may generate, control, or modify a field current forthe alternator 11 based on the profile that describes the periodicfluctuation in the operating characteristic for the generator 100. Thefield current may flow through a coil of wire coiled around a magneticconductive material. The magnetic conductive material may form thestator or rotor of the alternator 11. As the field current is increasedor decreased the output of the generator 100 fluctuates proportionally.Accordingly, speed fluctuations of the engine 13, which would normallylead to output fluctuations, may be countered by increasing ordecreasing the field current. The controller 10 may generate and apply apositive voltage, or increase the voltage, to the alternator 11 toincrease the field current during at least one portion of the profileand/or apply a negative voltage, or decrease the voltage, to thealternator 11 to decrease the field current during at least one portionof the profile.

The generator 100 may also include one or more of a fuel supply, acooling system, an exhaust system, a lubrication system, and a starter.Additional, different, or fewer components may be included. Thealternator 11 may include an electromechanical rotating magnetic fieldand a stationary armature, a rotating armature with a stationarymagnetic field, or a linear alternator. The engine 13 may be powered bygasoline, diesel fuel, or gaseous fuel. Examples of gaseous fuels may beliquefied petroleum gas (LPG), hydrogen gas, natural gas, biogas, oranother gas. Examples of LPG may be or include primarily butane,primarily propane, or a mixture of hydrocarbon gases. The hydrogen gasmay include hydrogen mixed with air or oxygen. The hydrogen gas may bemixed with another fuel when delivered to the engine 13. Natural gas(e.g., compressed natural gas (CNG)) may be a hydrocarbon gas mixture.Biogas may be a gas produced by the breakdown of organic material. Othervariations are possible.

FIG. 2 illustrates an example speed profile for a generator. The speedprofile may be continuous or discrete. The speed profile may fluctuatebetween a maximum frequency and a minimum frequency. The frequency maybe measured in rotations per unit time. The speed profile may be afunction of the combustion cycle of the engine 13 and/or the physicalconstruction of the generator. The speed profile may be periodic. Theperiod of the speed profile (Tp) may depend on the diameter of the rotoror the average speed of the alternator 11. The circumference of therotor divided by the average frequency (rotations per unit time)provides the amount of time for one rotation, which may be the period ofthe speed profile (Tp).

The speed profile may be based on a set of samples taken or made by thedetection circuit 15. The samples may be made at a predeterminedinterval (Ts). The interval Ts may be constant or variable. Examplevalues for the interval Ts include 5 milliseconds, 10 milliseconds, 16milliseconds, 16.7 milliseconds, 17 milliseconds, 20 milliseconds oranother value. The interval Ts may be selected based as the inverse ofthe frequency of the output of the generator (e.g., 1/50 Hz=20milliseconds, 1/60 Hz=16.7 milliseconds). The interval Ts may beselected based on a user input or in various other ways.

The speed profile may be a discrete or piecewise function and have anumber of segments corresponding to the number of measurement samples.For example, FIG. 2 includes four repeating segments A, B, C, and D,each having a horizontal length that corresponds to interval Ts. Theabsolute minimum and maximum values for the speed profile may notcoincide in time with the samples. The interval Ts may be varied inorder to determine locations the absolute maximum value and/or theabsolute minimum value. For example, the interval Ts may be increased insmall increments in order to identify an interval Ts that intersects theabsolute maximum value and/or the absolute minimum value of the speedprofile.

FIG. 3 illustrates an example output produced by an alternator of agenerator operating under the speed profile of FIG. 2. The output of thealternator may be measured in voltage, current, or power. The output maybe proportional to the speed profile or have a shape congruent to theshape of the speed profile.

The output may be considered congruent to the speed profile based on therelative change in ratios between the speed profile and the output. Inone example, the two shapes are considered congruent based on the ratiosto the minimum values and maximum values of the shapes. For any period,the ratio of the maximum value of the speed profile value to the maximumvalue of the output is calculated and the ratio of the minimum value ofthe speed profile value to the minimum value of the output iscalculated. When the difference between the ratios is within apredetermined range, the two shapes are considered congruent. Examplesfor the predetermined range include 0.8 to 1.05 and 0.9 to 1.1. Inaddition or in the alternative, the two shapes may be consideredcongruent when one or more maximum values of the speed profile occurwithin a predetermined time period of one or more maximum values of theoutput and/or one or more minimum values of the speed profile occurwithin a predetermined time period of one or more minimum values of theoutput. Example predetermined time periods include 5 milliseconds and 10milliseconds.

FIG. 4 illustrates an example modified field current according to thespeed profile of FIG. 2. The controller 10 may identify the speedprofile of the engine, such as through detecting the engine speed,monitoring an output voltage, current, or power, or by using date orinformation about an engine type or speed from a look-up table. Thecontroller 10 may control the field current as shown in FIG. 4 tocounteract the fluctuations in the engine speed or output voltage,current, or power. The speed profile of FIG. 2 is illustrated to showthe changes in the modified field current track changes in the speedprofile. The modified field current may be inversely proportional to thespeed profile. The inversely proportional relationship may be constantthroughout period Tp or may fluctuate with a predetermined range. Thepredetermined range may be plus or minus any percentage value from 1% to15%. As the field current and engine speed fluctuations counteract eachother, fluctuations in the output voltage may be reduced and the outputvoltage may be nearly constant.

In another example, the modified field current may be inverselycongruent to the speed profile. In one example, the two shapes areconsidered inversely congruent based on the ratios to the minimum valuesand maximum values of the shapes. For any period, the ratio of themaximum value of the speed profile value to the corresponding minimumvalue of the output is calculated and the ratio of the minimum value ofthe speed profile value to the corresponding maximum value of the outputis calculated. When the difference between the ratios is within apredetermined range, the two shapes are considered inversely congruent.Examples for the predetermined range include 0.8 to 1.05 and 0.9 to 1.1.In addition or in the alternative, the two shapes may be consideredinversely congruent when one or more maximum values of the speed profileoccur within a predetermined time period of one or more minimum valuesof the output and/or one or more minimum values of the speed profileoccur within a predetermined time period of one or more maximum valuesof the output. Example predetermined time periods include 5 millisecondsand 10 milliseconds.

It should be appreciated that the systems and methods of field currentcontrol to establish more constant output voltage may additionally oralternatively be performed to counter or reduce output voltagevariations caused by various other issues known or unknown, includingfluctuations caused by the shape of the rotor.

FIGS. 5 and 6 illustrate another example using continuous functions. Thefield current control may be activated and deactivated according to acontrol signal. The control signal may be generated based oninstructions received from a user, a predefined schedule, or a feedbackcontrol system. The user may activate or deactivate the field currentcontrol through a switch, button, or other setting on the generator 100or controller 10, which triggers the control signal. The user mayremotely send a command to the generator controller 10 through a mobileapplication or a website. The predefined schedule may activate the fieldcurrent control during peak hours and deactivate the field currentcontrol outside of peak hours. The feedback control system may monitorthe output of the generator (e.g., voltage sensor or current sensor) andactivate the field current control when the output exceeds a thresholdvalue. The threshold value may be a percentage of the average output(e.g., 5% or 10%), a number of standard deviations from the mean output(e.g., 1 standard deviation), or a set value (e.g., 100 volts, 130volts).

FIG. 5 illustrates an example comparison of field current, outputvoltage, and frequency for a generator when the control signaldeactivates the field current control. FIG. 6 illustrates the example ofFIG. 5 with an example modified field current when the control signalactivates the field current control.

In FIG. 5, with the field current control deactivated, the field currentis constant, as shown by the dotted line 251. The output voltage may bea root mean squared (RMS) value or a peak voltage value. The outputvoltage, as shown by the dashed line 253, may fluctuate for variousreasons, such as in accordance with variations in the frequency or speedof the engine or alternator, as shown by the solid line 255. Thecontroller 10 may identify or detect the output voltage, such as througha feedback signal or predefined schedule. In FIG. 6, with the fieldcurrent control activated, the field current is controlled to fluctuatein an inverse relationship to the frequency or speed of the alternator.The field current may be controlled to fluctuate between a maximumcurrent and a minimum current. Examples include 1.19 amps for theminimum current and 1.21 amps for the maximum current over each intervalTs (e.g., 16.7 milliseconds). Accordingly, the output voltage, as shownby dashed line 253, becomes relatively constant (e.g., within afluctuation tolerance).

FIG. 7 illustrates another example modified field current. The modifiedfield current of FIG. 7 corresponds to a speed profile for the engine 13in partial load. When the engine 13 is in partial load, the interval Tsand the period Tp may not change. However, the maximum value and minimumvalue may fluctuate (or amplitude D of the speed profile may decrease)as a function of the load. The controller 10 may identify the instanceof partial load, such as through a load monitoring system or a feedbackcontrol system, and may decrease the range of the field currentproportionally.

In one example, the generator controller 10 may store multiple speedprofiles that correspond to possible loads on the engine 13. Themultiple speed profiles may include a low load speed profile, a mediumload speed profile, and a high load speed profile. Each of the multiplespeed profiles may be derived through operating the engine 13 at acorresponding load. The variance of the speed profile may varyproportionally to the load on the engine 13. The controller 10 maygenerate or access a speed profile using a closed loop feedback fordetecting the load on the engine 13 or through a lookup table foravailable speed profile. As the load on the engine 13 increases, morepower may be demanded and more gas may be compressed, which slows downthe engine 13. When the engine 13 is significantly slowed down, theengine 13 fires harder and speeds up more.

The variation of the speed profile may be a function of the type ofengine, the inertia of the engine, and features of the engine (e.g.,turbocharger). A low variance may be about 1% between the absolutemaximum and absolute minimum in a period. A medium variance may varyabout 3%, and a high variance may vary about 6%. Other variances at anyvalue are possible.

The values that make up the speed profile may fluctuate according tocombustion cycles of the engine 13. Thus, the shape or variance of thespeed profile may be a function of the number of cylinders of the engine13. An engine with four or more cylinders may have a speed profile withlow variance because one cylinder out of the four or more cylinders isusually firing or approaching firing. That is, the crankshaft has lesstime to decelerate after a power stroke of one cylinder before a powerstroke of another cylinder begins. The combustion cycles of any onecylinder is balanced by the combustion cycles of the other cylinders.

On a single cylinder engine, the speed profile has a high variancebecause there are no other cylinders to balance the combustion cycles ofthe single cylinder. The compression stroke significantly slows down theengine (e.g., extracts power from the crank shaft) and the power strokesignificantly speeds up the engine (e.g., adds power to the crankshaft). The intake stroke and exhaust stroke may slow down the engine toa lesser extent.

In a two cylinder engine, the speed profile may have a medium variancefor reasons similar to the four cylinder engine discussed above.However, for a two cylinder odd fire engine, the speed profile may havea high variance (e.g., even higher than in the one cylinder example). Ina two cylinder odd fire engine, the cylinders fire close together intime. In one example, during the 360 degrees rotation of the crankshaft,the first cylinder fires at 270 degrees and the second cylinder fires at450 degrees (90 degrees of the subsequent cycle). The speed of thecrankshaft may reach a first maximum after the first cylinder fires anda second, higher maximum after the second cylinder fires.

The speed profile of an engine with an odd number of cylinders may havea variance because the cycles of the engine and the alternator may beout of synch. A three cylinder engine may fire every 240 degrees. Thealternator may be a two pole alternator that takes power every 180degrees or a four pole alternator that takes power every 90 degrees. Ineither case, there may be aliasing between the alternator and the enginebecause the engine fires and the alternator draws power at varying timesrelative to each other.

FIG. 8 illustrates an example output for a generator with field currentcontrol deactivated. Because the field current control is deactivated,the field current, as shown by dash line 411 is substantially constant.Window 401 illustrates the deviation between the alternator output, asshown by solid line 413, and a sine wave, as shown by the dotted line415.

Harmonics in the alternator output may contribute to the deviationbetween the alternator output and the sine wave. The harmonics may becaused by the geometric shape of the alternator. While a perfectalternator may be a perfectly round device that provides a perfectsinusoid, such an alternator would be very inefficient and difficult tomanufacture. In practice, windings of the alternator have a pitch thatis not uniform (unity). The rotor cannot be perfectly round nor can thestator be a full pitch. The resulting waveform is imperfect. The shapeof the resulting waveform may be expressed as a sum of sinusoids ofvarying order.

The periodic wave form can be expressed as a sum of odd orderedsinusoids of varying frequency. In one example, the first order sinusoidhas a frequency of 50 or 60 Hz, the third order has a frequency of 150or 180 Hz, and so on. Detectable harmonics may include the 5^(th) order,the 7^(th) order, the 9^(th) order, the 11^(th) order, and/or otherharmonics. Because of the saturation in the core of the alternator, theattenuation of each harmonic increase logarithmically. Thus, the 3^(rd)and 5^(th) harmonics are the most detectable.

The field current profile may be adjusted to reduce the distortioncaused by the harmonics, which may be referred to as total harmonicdistortion (THD), to a threshold level. Example THD thresholds include1%, 2%, 5% and 10%. Without field current control, design of a generatorto meet the 1%, 2%, or even 5% THD threshold would involve very highinefficiency. However, controlling or fine tuning the field currentprofile may eliminate or reduce the effects of the harmonics in theoutput and meet very low THD thresholds.

FIG. 9 illustrates the example output of FIG. 8 with a modified fieldcurrent, shown by dotted line 417. The sine wave, shown by solid line419, is unchanged from FIG. 8. However, the alternator output, shown bysolid line 421, overlaps the sine wave. Thus, solid line 419 and 421appear as a single line. The modified field current may have manydifferent shapes. The shape may have multiple harmonics inverselyrelated to the harmonics originally in the alternator output. Themodified field current may have multiple minimums and maximums in eachperiod. The change in output of the alternator (e.g., voltage, current,or power) is proportional to the field current of the alternator.

The modified field current may be varied at a higher amplitude to reduceharmonics than in the speed profile examples. The variance in themodified field current to reduce harmonics may be about 1.08 to 1.26 amprange over a 2 millisecond interval, as compared to a 1.19 to 1.21 amprange over a 16.7 millisecond interval discussed above with respect tosome speed profile correction examples.

In some systems, the controller 10 may control the field current inaccordance with predetermined settings or initial detections ofgenerator parameters. In other systems, the controller 10 may monitorgenerator parameters (such as engine or alternator speed, outputvoltage, output current, or output power) continuously, periodically,randomly, when triggered, or at other times, and may modify the fieldcurrent profile in accordance with any identified changes in themonitored parameters. Other variations are possible.

FIG. 10 illustrates an example regulator circuit for implementingcurrent profile control. The inductor 301 may correspond to the fieldcoil 17 of the alternator 11 of the generator 100. The coil includes afield positive portion F_(pos) and a field negative portion F_(neg). Apower source 303 supplies energy to the energy receiving unit 311. Theenergy receiving unit 311 may be a capacitor or another storage element.The diodes 305 may restrict a direction of flow in one path through theregulator circuit. Switches 307 may open and close another path throughthe regulator circuit. FIG. 11 illustrates another example regulatorcircuit in which the switches 307 are field effect transistors 317.Example components for the switches 307 also include operationalamplifier, switch circuit, relay, or other types of transistors such asmetal-oxide-semiconductor field effect transistor (FET), bipolarjunction transistors, unijunction transistor, or thin film transistors.

FIG. 12 illustrates the example regulator circuit of FIG. 11 in a firststate. In the first state, the switches 307 are closed, which allowscurrent from the source 303 to flow through the inductor 301, as shownby arrows 310. The current through the inductor 301 in the first stateflows from F_(pos) to F_(neg) (left to right in FIG. 12). FIG. 13illustrates the example regulator circuit of FIG. 11 in a second state.In the second state, the switches 307 are open, which prevents currentfrom the source 303 to flow through the inductor 301. However, if energyis stored in the inductor 301, current may flow from inductor 301 to theenergy receiving unit 311, as shown by arrows 312. The current throughthe inductor 301 in the second state flows from F_(neg) to F_(pos) (leftto right in FIG. 13).

The controller 10 may generate a switch command for driving the switches307 (or FET 317) based on the profile for the generator 100. The switchcommand causes the switches to turn on and off, defining a duty cycle.The controller 10 increases the duty cycle of the switch command duringat least one portion of the profile. For example, the switch command maybe increased during positive slopes of the profile. The controller 10decreases the duty cycle of the switch command during at least one otherportion of the profile. For example, the switch command may be decreasedduring negative slopes of the profile. The switch command drives theactive regulator in response to the switch command.

FIG. 14 illustrates an example duty cycle for a switch command 341 ofthe regulator circuit. The switch command 341 is set at a duty cyclebetween a high voltage (V_(H)) and a low voltage (V_(L)) in order tokeep the field current at a target level. The first state and the secondstate are indicated by the encircled numbers (1) and (2). The width ofthe first state and the second state may be a predetermined time period(e.g., 1 millisecond or another value). In the first state, the fieldcurrent 343 in the inductor 301 increases, and in the second state thefield current 343 in the inductor 301 decreases. To move the fieldcurrent 343 from one level to another (e.g., from TARGET 1 to TARGET2),one of the high voltage or low voltage may (first state or second state)may be active for a longer time period. In one example, when the dutycycle is about 50%, the field current 343 stays constant (or decreasesslightly), when the duty cycle is above 50%, the field current 343increases, and when the duty cycle is below 50%, the field current 343decreases.

The active regulator circuit allows for precision and quick adjustmentsto the current through the inductor 301. If a typical switch were usedto control the field current 343 through the inductor 301, thenegatively sloped portion of field current 343 would be a slow decay(e.g., exponential decay) driven by the internal resistance of theinductor 301. That is, normally the operation of the inductor 301resists current changes in short amounts of time. However, the activeregulator circuit actively controls the field current by increasing theamounts of time that current is drawn from the inductor 301. The activeregulator draws current from the inductor 301 using the energy receivingunit 311. The active regulator may control the field current 343 totrack the engine profile at high speed rates (e.g., 1.0 amp per secondor greater).

The active regulator circuit may control the field current 343 to reducefluctuation in output from speed variations in the engine and from totalharmonic distortion. One or both of the phenomena may be reduced bygenerating the switch command that tracks the expected current profile.In one example, the switch command may control adjustments at a lowinterval (e.g., on the order of every 10-20 milliseconds) to addressexpected changes in speed variation and adjustments at a high interval(e.g., on the order of every 1-2 milliseconds) to address expectedfluctuations caused from harmonic distortion.

FIG. 15 illustrates an example generator controller 10. The generatorcontroller 10. The generator controller 10 may include a processor 300,a memory 352, and a communication interface 353. The generatorcontroller 10 may be connected to a workstation 359 or another externaldevice (e.g., control panel) and/or a database 357. Optionally, thegenerator controller 10 may include an input device 305 and/or a sensingcircuit 311. The sensing circuit 311 receives sensor measurements fromthe detection circuit 15. Additional, different, or fewer components maybe included.

The memory 352 may store a profile for a generator that describes aperiodic fluctuation in an operating characteristic for the generator.The profile may track one of the inputs to the generator such as speedof the crankshaft or one of the outputs to the generator such asvoltage, current, or power. The memory 352 may store multiple profiles.The profiles may be associated with different types of generators,different loads, different operating environments, or different sets ofoutput tolerances.

The profiles in the memory 352 may be constant. For example, theprofiles may be preloaded by a manufacturer. Alternatively, the profilesmay be adjusted over time. The profiles may be adjusted based on thelife cycle of the generator to account changes based on deterioration orservice. The profiles may be adjusted in real time or near real time. Anear real time adjustment is when measurements taken a short amount oftime (e.g., 1 second, 10 second, or 1 minute) in the past are used togenerate a profile for the near future. For example, the average profiledetected over the last minute may be continuously updated and stored asthe current profile for the generator.

The processor 300 may access the profile and control, based on theprofile, a field current for an alternator associated with thegenerator. The processor 300 may generate a switching command having aduty cycle that tracks the slope of the profile. For example, when theprofile increases, which indicative of an increasing generator output,the duty cycle slows in order to reduce the field current for thealternator, which tends to decreases the generator output. The resultingoutput may approach a sinusoid. The RMS value of the resulting outputmay approach a constant value.

The profile for the generator may be entered manually. For example, thecommunication interface 303 receives data indicative of profile from anetwork (e.g., the Internet), an external database 357, a control panelor other input device 355, or from the workstation 359. In addition orin the alternative, the communication interface 353 may receive aschedule for activating or deactivating the field current control, an areal time command for activating or deactivating the field currentcontrol, a modification to one of the profiles, or a THD threshold froma network (e.g., the Internet), an external database 357, a controlpanel or other input device 355, or from the workstation 359. The inputdevice 355 may be a flicker toggle switch that the user activates whenflicker becomes noticeable.

The generator controller 10 may control multiple generators. The memory352 may include profiles for multiple generators, and the processor 300may generate field current profiles for multiple generators. In oneexample, the generators are parallel generators that are mechanicallyconnected via crankshafts and electrically connected via a bus. In thiscase, the field current profiles may be identical or vary only to theextent of the physical differences between generators. The generatorcontroller 10 may also generate switch commands to couple and decouplethe generators from the bus. The controller may be internal to orconnected with one or more of the generators, included in a standalonedevice, in or connected with another device such as an automatictransfer switch, or in various other devices, locations, or connections.

In another example, the generators are not mechanically connected andmay be assigned varying current profiles based on both the respectivespeeds of the engines and the physical differences between generators. Acommunication line may facilitate data communication between generatorcontrollers. The communication may be Modbus or another protocol.

FIG. 16 illustrates example flowchart for field current control. Themethods in FIG. 16 may, in some instances, be implemented as logic orsoftware executable by a controller, such as generator controller 10.Additional, different, or fewer acts may be provided. The acts may beperformed in the order shown or other orders. The acts may also berepeated.

At act S101, the controller measures an operating characteristic of anengine. The operating characteristic may be the speed of the engine, anoutput current, voltage, or power, or various other characteristics. Atact S103, the controller identifies a periodic fluctuation based on themeasurements. In one example, the measurements are sampled at a sampleinterval. The sample interval may be equivalent to, or divide evenlyinto, the period of the engine. Thus, a set of samples may beconstructed into a periodic fluctuation. In another example, the sampleinterval may not divide into the period of the engine, but may bemanipulated to identify the period of the engine.

For example, the controller may identify multiple cycles from the set ofsamples and calculate an average of corresponding points from themultiple cycles. The engine profile is generated from the average of thecorresponding points.

At act S105, the controller develops or generates an engine profile thatdescribes the periodic fluctuation of the operating characteristic ofthe engine. When the operating characteristic is speed, the periodicfluctuation may be based in part on the combustion cycles of the engine.

At act S107, the controller generates a switch command based on theengine profile. The switch command may be selected to follow the engineprofile. In one example, a duty cycle of the switch command is increasedfor positively sloped portions of the engine profile and decreased fornegatively sloped portions of the engine profile.

At act S109, the controller adjusts a field current for an alternatorassociated with the engine in response to the field current profile. Forexample, the controller may send the switch command to a regulatorcircuit that activates and deactivates one or more power sources with afield coil of the alternator. The switch command may activate one ormore switches to increase current flow to the field coil and deactivateone or more switches to decrease current flow to the field coil. Theswitch command may activate one or more first switches to increasecurrent flow to the field coil and activate one or more second switchesto decrease current flow to the field coil.

In other variations, the controller may identify an engine type, make,or model, and may look up a predetermined engine profile based on theidentified engine type, make, or model. The controller may generate afield current profile in accordance with the identified predeterminedengine profile. In still other examples, the controller may look up apredefined field current profile based on the identified engine type,make, or model. In any of these examples, the system may perform actS109 thereafter. Other variations are possible.

The processor 300 may include a general processor, digital signalprocessor, an application specific integrated circuit (ASIC), fieldprogrammable gate array (FPGA), analog circuit, digital circuit,combinations thereof, or other now known or later developed processor.The processor 300 may be a single device or combinations of devices,such as associated with a network, distributed processing, or cloudcomputing.

The memory 352 may be a volatile memory or a non-volatile memory. Thememory 352 may include one or more of a read only memory (ROM), randomaccess memory (RAM), a flash memory, an electronic erasable program readonly memory (EEPROM), or other type of memory. The memory 352 may beremovable from the network device, such as a secure digital (SD) memorycard.

In addition to ingress ports and egress ports, the communicationinterface 303 may include any operable connection. An operableconnection may be one in which signals, physical communications, and/orlogical communications may be sent and/or received. An operableconnection may include a physical interface, an electrical interface,and/or a data interface.

The communication interface 353 may be connected to a network. Thenetwork may include wired networks (e.g., Ethernet), wireless networks,or combinations thereof. The wireless network may be a cellulartelephone network, an 802.11, 802.16, 802.20, or WiMax network. Further,the network may be a public network, such as the Internet, a privatenetwork, such as an intranet, or combinations thereof, and may utilize avariety of networking protocols now available or later developedincluding, but not limited to TCP/IP based networking protocols.

While the computer-readable medium (e.g., memory 352 or database 357) isshown to be a single medium, the term “computer-readable medium”includes a single medium or multiple media, such as a centralized ordistributed database, and/or associated caches and servers that storeone or more sets of instructions. The term “computer-readable medium”shall also include any medium that is capable of storing, encoding orcarrying a set of instructions for execution by a processor or thatcause a computer system to perform any one or more of the methods oroperations disclosed herein.

In a particular non-limiting, exemplary embodiment, thecomputer-readable medium can include a solid-state memory such as amemory card or other package that houses one or more non-volatileread-only memories. Further, the computer-readable medium can be arandom access memory or other volatile re-writable memory. Additionally,the computer-readable medium can include a magneto-optical or opticalmedium, such as a disk or tapes or other storage device to capturecarrier wave signals such as a signal communicated over a transmissionmedium. A digital file attachment to an e-mail or other self-containedinformation archive or set of archives may be considered a distributionmedium that is a tangible storage medium. Accordingly, the disclosure isconsidered to include any one or more of a computer-readable medium or adistribution medium and other equivalents and successor media, in whichdata or instructions may be stored. The computer-readable medium may benon-transitory, which includes all tangible computer-readable media.

In an alternative embodiment, dedicated hardware implementations, suchas application specific integrated circuits, programmable logic arraysand other hardware devices, can be constructed to implement one or moreof the methods described herein. Applications that may include theapparatus and systems of various embodiments can broadly include avariety of electronic and computer systems. One or more embodimentsdescribed herein may implement functions using two or more specificinterconnected hardware modules or devices with related control and datasignals that can be communicated between and through the modules, or asportions of an application-specific integrated circuit. Accordingly, thepresent system encompasses software, firmware, and hardwareimplementations.

In accordance with various embodiments of the present disclosure, themethods described herein may be implemented by software programsexecutable by a computer system. Further, in an exemplary, non-limitedembodiment, implementations can include distributed processing,component/object distributed processing, and parallel processing.Alternatively, virtual computer system processing can be constructed toimplement one or more of the methods or functionality as describedherein.

As used in this application, the term ‘circuitry’ or ‘circuit’ refers toall of the following: (a) hardware-only circuit implementations (such asimplementations in only analog and/or digital circuitry) and (b) tocombinations of circuits and software (and/or firmware), such as (asapplicable): (i) to a combination of processor(s) or (ii) to portions ofprocessor(s)/software (including digital signal processor(s)), software,and memory(ies) that work together to cause an apparatus, such as amobile phone or server, to perform various functions) and (c) tocircuits, such as a microprocessor(s) or a portion of amicroprocessor(s), that require software or firmware for operation, evenif the software or firmware is not physically present.

This definition of ‘circuitry’ applies to all uses of this term in thisapplication, including in any claims. As a further example, as used inthis application, the term “circuitry” would also cover animplementation of merely a processor (or multiple processors) or portionof a processor and its (or their) accompanying software and/or firmware.The term “circuitry” would also cover, for example and if applicable tothe particular claim element, a baseband integrated circuit orapplications processor integrated circuit for a mobile phone or asimilar integrated circuit in server, a cellular network device, orother network device.

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andanyone or more processors of any kind of digital computer. Generally, aprocessor may receive instructions and data from a read only memory or arandom access memory or both. The essential elements of a computer are aprocessor for performing instructions and one or more memory devices forstoring instructions and data. Generally, a computer may also include,or be operatively coupled to receive data from or transfer data to, orboth, one or more mass storage devices for storing data, e.g., magnetic,magneto optical disks, or optical disks. Computer readable mediasuitable for storing computer program instructions and data include allforms of non-volatile memory, media and memory devices, including by wayof example semiconductor memory devices, e.g., EPROM, EEPROM, and flashmemory devices; magnetic disks, e.g., internal hard disks or removabledisks; magneto optical disks; and CD ROM and DVD-ROM disks. Theprocessor and the memory can be supplemented by, or incorporated in,special purpose logic circuitry.

The illustrations of the embodiments described herein are intended toprovide a general understanding of the structure of the variousembodiments. The illustrations are not intended to serve as a completedescription of all of the elements and features of apparatus and systemsthat utilize the structures or methods described herein. Many otherembodiments may be apparent to those of skill in the art upon reviewingthe disclosure. Other embodiments may be utilized and derived from thedisclosure, such that structural and logical substitutions and changesmay be made without departing from the scope of the disclosure.Additionally, the illustrations are merely representational and may notbe drawn to scale. Certain proportions within the illustrations may beexaggerated, while other proportions may be minimized. Accordingly, thedisclosure and the figures are to be regarded as illustrative ratherthan restrictive.

While this specification contains many specifics, these should not beconstrued as limitations on the scope of the invention or of what may beclaimed, but rather as descriptions of features specific to particularembodiments of the invention. Certain features that are described inthis specification in the context of separate embodiments can also beimplemented in combination in a single embodiment. Conversely, variousfeatures that are described in the context of a single embodiment canalso be implemented in multiple embodiments separately or in anysuitable sub-combination. Moreover, although features may be describedabove as acting in certain combinations and even initially claimed assuch, one or more features from a claimed combination can in some casesbe excised from the combination, and the claimed combination may bedirected to a sub-combination or variation of a sub-combination.

One or more embodiments of the disclosure may be referred to herein,individually and/or collectively, by the term “invention” merely forconvenience and without intending to voluntarily limit the scope of thisapplication to any particular invention or inventive concept. Moreover,although specific embodiments have been illustrated and describedherein, it should be appreciated that any subsequent arrangementdesigned to achieve the same or similar purpose may be substituted forthe specific embodiments shown. This disclosure is intended to cover anyand all subsequent adaptations or variations of various embodiments.Combinations of the above embodiments, and other embodiments notspecifically described herein, will be apparent to those of skill in theart upon reviewing the description.

It is intended that the foregoing detailed description be regarded asillustrative rather than limiting and that it is understood that thefollowing claims including all equivalents are intended to define thescope of the invention. The claims should not be read as limited to thedescribed order or elements unless stated to that effect. Therefore, allembodiments that come within the scope and spirit of the followingclaims and equivalents thereto are claimed as the invention.

I claim:
 1. A method comprising: identifying a profile for a generator,wherein the profile describes a periodic fluctuation in an operatingcharacteristic for the generator; and controlling, based on the profile,a level of a field current for an alternator associated with thegenerator, wherein the operating characteristic describes an output ofthe alternator, and the periodic fluctuation includes harmonics causedby operation of the alternator.
 2. The method of claim 1, wherein theprofile depends on a load on the engine in addition to the operatingcharacteristic.
 3. The method of claim 1, wherein the profile fluctuatesaccording to combustion cycles of the engine.
 4. The method of claim 1,further comprising: generating a switch command based on the profile forthe generator, wherein controlling the field current of the alternatorcomprises: increasing a duty cycle of the switch command during at leastone portion of the profile; and decreasing the duty cycle of the switchcommand during at least one portion of the profile.
 5. The method ofclaim 4, further comprising: driving an active regulator in response tothe switch command.
 6. The method of claim 1, wherein controlling thefield current of the alternator comprises: applying a positive voltageto the alternator to increase the field current during at least oneportion of the profile; and applying a negative voltage to thealternator to decrease the field current during at least one portion ofthe profile.
 7. The method of claim 1, wherein an output voltage of thealternator is proportional to the field current of the alternator.
 8. Anapparatus comprising: a memory configured to store a profile for agenerator, wherein the profile describes a periodic fluctuation in anoperating characteristic for the generator; and a controller configuredto access the profile and control, based on the profile, a level of afield current for an alternator associated with the generator, whereinthe operating characteristic describes an output of the alternator, andthe periodic fluctuation includes harmonics caused by operation of thealternator.
 9. The apparatus of claim 8, further comprising: a regulatorcircuit electrically coupled to a field coil of the alternator, whereinthe field current is in a first direction during a first portion of theprofile, and the field current is in a second direction during a secondportion of the profile.
 10. The apparatus of claim 9, wherein theregulator circuit includes a switching device configured to generate aswitch command based on the profile for the generator.
 11. The apparatusof claim 10, wherein a duty cycle of the switch command increases duringat least one portion of the profile and decreases during at least oneportion of the profile.
 12. The apparatus of claim 8, furthercomprising: a detection circuit configured to collect a plurality ofsamples according to a predetermined time period, wherein the profile isgenerated, at least in part, from the plurality of samples.
 13. Theapparatus of claim 8, wherein the operating characteristic depends on aspeed of an engine of the generator, and the periodic fluctuationdescribes combustion cycles of the engine.
 14. A method comprising:identifying a speed profile for an engine, wherein the speed profiledescribes a periodic fluctuation in operating speed for the engine basedin part on combustion cycles of the engine; generating a field currentprofile based on the speed profile; and adjusting a field current for analternator associated with the engine in response to the field currentprofile.
 15. The method of claim 14, further comprising: generating aswitch command based on the field current profile; increasing a dutycycle of the switch command during a first portion of the speed profile;and decreasing the duty cycle of the switch command during a secondportion of the speed profile.
 16. The method of claim 14, furthercomprising: measuring a set of samples from a speed detection circuit,wherein the speed profile is generated, at least in part, from the setof samples.
 17. The method of claim 16, further comprising: identifyingmultiple cycles from the set of samples; and calculating an average ofcorresponding points from the multiple cycles, wherein the speed profileis generated from the average of the corresponding points.